The effects of sublethal pentachlorophenol exposure on predation risk in freshwater rotifer species

Abstract

The effects of anthropogenic toxicants on predator–prey interactions is a poorly understood subject in ecotoxicology. Ecological studies of invertebrate predator–prey systems have indicated that the body size, swimming behavior, and population density of both predator and prey are important components influencing predation risk. However, weighing the relative contribution of predation risk factors, the manner in which they interact, and their responses to toxicant exposure requires multi-species predator–prey systems which consider both empirical measures of predator efficiency as well as the behavior of predator and prey. The effect of pentachlorophenol (PCP) on the vulnerability of six herbivorous freshwater rotifer species to predation by the predatory rotifer Asplanchna girodi was studied. Prey species were exposed to sublethal concentrations of PCP (0, 110, 190, and 330 μg/l) for 30 min. Predator–prey encounters and prey ingestions were quantified for each species and PCP concentration. In addition, a computer tracking system was used to assess the effects of PCP on the swimming speed of each species. Regression models indicated a relationship between predator–prey encounters and both prey body size and prey swimming speed. However, swimming speed was dependent upon body size. The number of prey ingested was only slightly dependent upon the frequency of predator–prey encounters. Responses to PCP exposure varied between species, and the relationships between different indices of predation risk became less apparent after PCP exposure. Our results indicate that predator–prey interactions are responsive measures of toxicant exposure and provide ecological insight into how toxicants modify predator–prey interactions and zooplankton community structure.